1. Field of the Invention
The present invention relates to zoom lenses used in image pickup apparatuses such as single-lens reflex cameras, digital cameras, video cameras, and film cameras.
2. Description of the Related Art
Image pickup apparatuses such as film cameras, digital cameras, and video cameras require a zoom lens having a high zoom ratio and high optical performance.
A positive lead type zoom lens, in which the most object-side lens unit has a negative refractive power, is known as a zoom lens of high zoom ratio.
There is known a high-zoom-ratio telephoto-type three-unit or four-unit zoom lens in which three or more lens units are moved for zooming (U.S. Pat. Nos. 5,530,594, 6,052,235, 6,483,649, and 6,778,331, and Japanese Patent Laid-Open No. 2005-266183).
Many of telephoto type zoom lenses including a long focal length are large and heavy. Therefore, when a telephoto type zoom lens is used, it is difficult to photograph with the vibration of the zoom lens controlled.
Inclination of the zoom lens due to vibration causes a photographed image to be displaced (blurred) by an amount according to the inclination angle and the focal length at the zooming position. Some of telephoto type zoom lenses have image stabilizing performance to prevent blurring of a photographed image.
There is known as a zoom lens having image stabilizing performance. The zoom lens has, in order from the object side to the image side, first, second, and third lens units having positive, negative, and positive refractive powers, respectively. The whole second lens unit is vibrated in a direction perpendicular to the optical axis so as to obtain a still image (U.S. Pat. Nos. 5,715,088 and 7,123,422).
In general, in zoom lenses, increasing the refractive power of each lens unit reduces the moving distance of each lens unit for obtaining a predetermined zoom ratio, thereby facilitating achieving a high zoom ratio with the overall length of the lens reduced.
However, simply increasing the refractive power of each lens unit and reducing the moving distance of each lens unit increases the aberration fluctuation accompanying the zooming. Particularly in the case of a high zoom ratio, it is difficult to obtain excellent optical performance throughout the entire zoom range.
The zoom lenses described in the above references (U.S. Pat. Nos. 5,530,594, 6,052,235, 6,483,649, and 6,778,331, and Japanese Patent Laid-Open No. 2005-266183) consist of three or four units and have a comparatively small number of lenses, and the whole systems thereof are small. However, the zoom ratios of the zoom lenses are about four times and insufficient.
On the other hand, in a zoom lens having image stabilizing performance, an inappropriate lens configuration of image stabilizing lens units moved for image stabilization increases the amount of decentration aberration and decreases the optical performance under image stabilization.
Particularly in telephoto type zoom lenses, a large amount of decentration aberration occurs in image stabilization on the telephoto side, and this is difficult to correct.